1. Field of the Invention
The present invention relates to a method for manufacturing an optical waveguide receiver and an optical waveguide receiver.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2007-180425 discloses a semiconductor device. The semiconductor device includes a photodiode and capacitor disposed on a common substrate. The capacitor includes an n-type indium gallium arsenide (InGaAs) layer, a silicon nitride (SiN) layer disposed on the n-type InGaAs layer, a metal layer which is disposed on the SiN layer and which is made of titanium/platinum/aluminum (Ti/Pt/Au), an SiN layer disposed on the metal layer, and a metal layer which is disposed on this SiN layer and which is made of Ti/Pt/Au. The n-type InGaAs layer, which is included in the capacitor, is composed of a semiconductor layer common to the photodiode.
In recent years, optical waveguide receivers including a photodiode and optical waveguide integrated on a semiconductor substrate have been investigated. Such an optical waveguide receiver is used in high-speed optical communications having a high bit rate of, for example, 40 Gb/s or more. In particular, the optical waveguide receiver is used as a receiver front-end for a digital coherent communication system. The digital coherent communication system is an optical transmission system that combines a multi-level modulation technique with a digital coherent receiver technique. The optical waveguide receiver is manufactured by forming a butt-joint structure on a semiconductor substrate. In the butt-joint structure, a stacked semiconductor layer section constituting a photodiode and a stacked semiconductor layer section constituting an optical waveguide are butt-jointed with each other. An optical absorption layer including the stacked semiconductor layer section constituting the photodiode is optically coupled with a core layer including the stacked semiconductor layer section constituting the optical waveguide.